1. Field of the Invention
This invention relates to a slip forming process and to the monolithic, reinforced concrete structures produced in accordance with this slip forming process of this invention. More specifically, this invention relates to a process for slip forming reinforced concrete road structures, wherein the resulting slip formed structures have exposed reinforcing bars (“rebars”), which are partially embedded in and extend from within a slip formed, reinforced concrete structure. in one of the preferred embodiment of this invention, this slip forming process utilizes a “tunnel mold assembly” for forming a coping for bridge construction, wherein the coping is preferably formed concurrent with a slip formed concrete road bed pad. In this preferred embodiment of the invention, this slip formed coping includes both rebars embedded therein and exposed reinforcing bars extending from within the formed/finished coping. These exposed reinforcing bars are suitable for subsequent reinforcement and integration with additional in situ cast concrete structures. so as to further integrate such additional in situ cast concrete structures with the reinforced concrete road structures produced by this process.
2. Description of The Prior Art
Slip forming of concrete structures is a well-known technique for preparation of structural concrete elements for various industrial and public works (road, conduit, etc.) projects. Slip forming is a construction method in which concrete is poured into a continuously moving form. Slip forming is used for tall structures (such as bridges, towers, buildings, and dams), as well as horizontal structures, such as roadways. Slip forming enables continuous, non-interrupted, cast-in-place “flawless”, (i.e. no joints), concrete structures which have superior performance characteristics to piecewise construction, using discretely formed elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability, Concrete needs to be workable enough to be placed into the form and consolidated. (via vibration), yet quick-setting enough to emerge from the form with strength (also “self supporting strength” or “green strength”). This green strength is needed because the freshly set concrete must not only permit the form to “slip” upwards/forward. but also support the freshly poured concrete above it (“vertical slip forming”) and/or the freshly poured concrete in front of it (“horizontal slip forming”).
in vertical slip forming, the concrete on may be surrounded by a platform on which workers stand. placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together. the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip-form rises at a rate which permits the concrete to harden (develop green strength) by the time it emerges from the bottom of the form. In horizontal slip forming for pavement and traffic separation walls. concrete is laid down, vibrated, worked, and settled in place, while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.
The following is a representative (and not exhaustive) review of the prior art in this field:
U.S. Pat. No. 3,792,133 (to Goughnour issued Feb. 12, 1974) describes a method and an apparatus for concrete slip forming a highway barrier wall of varying transverse cross-sectional configuration for accommodating different grade levels on opposite sides of the wall, and wherein variations in the wail cross-sectional configuration may be readily accomplished during wail formation without requiring stopping, realignment or other interruptions in the screed movement during wall forming.
U.S. Pat. No. 4,266,917 (to Godbersen issued Mar. 12, 1981) describes a method for the efficient slip forming of highway median barrier wails of differing, size (adjustable height) and shape having any arrangement of linear and curved sections and while the machine is being advanced in a single direction. The lateral adjustability of opposite side walls of the form, relative to the top wall, permits the use of the side walls with top wails of varying widths. The relative vertical adjustment of the top wall and side walls provides for a wide variation in the vertical height of a barrier will particularly where a glare shield is to be formed on the barrier wall top surface. The slip forming of the glare shield takes place simultaneously and continuously with the slip forming of the barrier wall and over any selected portion of the wail while the machine is being advanced in a single direction. At any adjusted position of the slip form, the skirt member associated with each side wall is adjustable to prevent any flow of concrete from between the ground or highway surface and the form.
U.S. Pat. No. 4,084,948 (to Petersik issued Apr. 18, 1978) describes an improved barrier forming apparatus and method whereby a barrier is formed continuously over a surface, the barrier having continuous reinforcing rods extending the length of the barrier and having cagereinforced standard supports at predetermined intervals along the length of the barrier. The Petersik improved barrier forming assembly comprising a concrete forming member having a form cavity extending there through; a concrete passing member having a concrete delivery opening for passing concrete or the like to the fibrin cavity; and a positioning assembly comprising a support shaft and a door Member pivotally supported at a forward end of the concrete forming member, the barrier being extrudable continuously via the form cavity forom a rearward end of the concrete forming member. The door member selectively is positionable to partially seal the form cavity at the forward end of the concrete forming member and has rod clearance channels through which the reinforcing rods pass through the door member into the harm cavity when the door member is so positioned to seal the form cavity. The rod clearance channels permit ie door member to clearingly pass the reinforcing rods to open the form cavity at the forward end of the concrete forming member to allow the free passage of the barrier forming assembly over the cage reinforced standard supports.
U.S. Pat. No. 5,290,492 (to Belarde, issued May 1, 1994) describes a system for continuously forming a concrete Structure (a) having a predetermined cross-sectional configuration, (b) which extends along an elongate path, and (c) includes art outer surface haying a textured pattern comprising concave or convex portions which extend other than just parallel to the elongate path. The system includes a frame, a first form assembly, a second form assembly, a drive system, and a support assembly.
As is evident from the above, there are number of alternatives for the slip forming of structures for use in road and bridge construction, The numerous alternative systems have their proponents and their detractors. In the context of selection of the more appropriate and efficient system, for example, for construction of retainer/barrier walls and/or glare shield concrete structures, time is money and often is reflected in the bidding process. More specifically, the bid letting on highway construction projects routinely include both penalty provisions for tardy completion and/or bonus payments thr early completion. Accordingly, efficiencies Which advance project completion, generally translate into cost saving. Thus, there is continuing efforts to automate, where possible, the fabrication of structural concrete components in highway construction; and, to standardize the process for the fabrication of roadway components and thereby simplify the bid letting on such proiects, particularly federally funded highway construction projects,
As is evident from the foregoing, and need not be belabored, the slip forming of structural concrete structures, including, concrete structures for highway construction, is well-known, Invariably, such slip formed highway structures are integrated into roadbeds, used as dividers for road beds and as components for bridges or overpasses for such road beds. The specifications for these concrete structures have and continue to become more uniform and/or have basic specifications in common, because of the advancements in construction methods, and the use of federal funds for such highway construction projects. For example, the specification for a concrete bridge coping must include exposed rehars for the integration into both the road bed, or with a barrier wall, which is to be erected thereupon, and integrated therewith.
Up to now, the standard or generally accepted techniques for the fabrication of bridge coping for an overpass on the highway, have required either the use of a pre-cast coping element (fabricated off-site),, and/or the manual casting of a coping on-site, utilizing traditional forms and concrete casting techniques. In the case of a pre-cast concrete coping element, the road bed of the overpass requires special preparation since the pre-cast element does not readily conform to the angle of incline or grade of a ramp or overpass and, therefore, imperfectly abut one another upon placement on the incline of the bridge overpass. Accordingly, additional installation expense is required to insure the connection of abutting pre-cast copings to one another to insure the formation of a unitary coherent structure.
Alternatively, the casting of an overpass/bridge coping, using the a manual process for forming the coping, specifically, traditional forms and concrete casting techniques, is preferably to the pre-cast coping, because the resulting coping is structurally continuous, and better conforms to the incline/grade of the ramp or overpass. Notwithstanding, the on-site casting, of a bridge coping, by traditional concrete casting technique, is very labor intensive and does not. without an inordinate amount of man power, lend itself to rapid fabrication and accelerated completion schedules. In each of the foregoing alternatives, the coping is formed with extending rebars for the later integration of the coping into a road bed pad and/or the attachment to a retaining wall. which can be later formed on the top of the coping.
Accordingly, there continues to exist the need to both simplify the on-site fabrication of a bridge coping, minimize the manual labor requirements, permit/accommodate accelerated construction schedules, and yet produces a structure which is both coherent (e.g. monolithic structure), and faithfully conforms to the angle of incline or grade of a road overpass, without additional extensive on-site preparation.